1. Field of the Invention
The present invention relates to a data transmission network having several devices interconnected via a passive transmission device, and more particularly to a network formed using a passive transmission device without an active distributor where each device connected to the passive transmission device includes a converter to control data transfer.
2. Description of the Related Technology
Especially in the area of process automation, for networking of hardware (see FIG. 2, where devices are labeled with reference number 1) field bus systems (reference number 2 of FIG. 2) are used which have been developed and designed especially for these applications. The devices are for example controls, drives, input or output systems. The field bus system is characterized by its mechanical durability, its invulnerability to electrical noise, and by installation, start-up and maintenance simplicity. The field bus system proves effective in the area of rough ambient conditions.
In the use of field bus systems there is a problem for the user in that there are a diversity and multiplicity of different field bus systems which may all be mutually incompatible. Communications beyond the boundaries of a field bus system is technically extremely complex and thus can have poor efficiency. Moreover the choice of a certain field bus system for the final user in practice has the disadvantage that he is tied to a single manufacturer; this in turn can entail disadvantages with respect to costs in procurement, maintenance and service. In field bus systems at present there are standard data transmission technologies (for example, ANSI-TIA-EIA-485-A) to which are added additional restrictions, for example methods of access to transmission devices, mechanical and electrical requirements for cable connectors and plugs, connector pin assignments, data rates, maximum numbers of devices on a field bus and allowable line lengths.
Along with field bus systems, especially in the field of office communications there can be a computer network ETHERNET which works according to standard IEEE 802.3/Iso/IEC 8802-3 specifications which together with Transmission Control Protocol/Internet Protocol (TCP/IP) has been developed into a dominant network technology enabling worldwide data communications using the Internet between the most varied devices (for example, Personal Computers (PC), workstations, mainframes with different operating systems, etc.). For example, as shown in FIG. 3, there can be network bus systems with active distributors. In these bus systems there are point-to-point connections in which the devices with reference numbers 1 are connected to an active distributor via connections 2. Here data are relayed from one device to another by active distributor 5.
Such an active distributor is not used in process automation or in general in applications of automation engineering, since these distributors represent an additional cost factor and also reduce the reliability of the entire system.